Memorial Sloan Kettering Cancer Center's (MSK) has notified the FDA of a fatal serious adverse event (SAE) associated with a patient in Phase 1 study of Atara Biotherapeutics Inc's (NASDAQ:ATRA) autologous mesothelin CAR T, ATA2271. 

• MSK has voluntarily paused enrollment of new patients in the study temporarily while additional information regarding the case is gathered and reviewed. 
• ATA2271 is an autologous chimeric antigen receptor (CAR) T-cell therapy targeting mesothelin currently under clinical investigation in malignant pleural mesothelioma. 
• The single case involved a patient with a history of multiple malignancies and other comorbidities. 
• Also See: Atara Bio Unveils Pivotal Data On T Cell Therapy Tabelecleucel In Transplant Patients.
• "We anticipate providing a further update in the coming weeks following further discussion and consultation with MSK," said Jakob Dupont, MD, Head of Global Research & Development at Atara. 
• The first six patients enrolled in the two lowest dose cohorts received either 1x106 cells/kg (patients 1-3) or 3x106 cells/kg (patient 4-6) intrapleural ATA2271. 
• No dose-limiting toxicities have been reported to date within these two cohorts. The reported patient event relates to the first patient in a higher-dose cohort (6x106 cells/kg).
• The temporary pause in ATA2271 study enrollment does not impact the IND-enabling work currently underway to advance ATA3271, a separate, off-the-shelf, allogeneic CAR-T therapy targeting mesothelin. 
• Price Action: ATRA shares are down 6.36% at $12.81 during the market session on the last check Friday.